Process for preparing nonwoven fabrics

ABSTRACT

D R A W I N G NONWOVEN FABRICS ARE PREPARED BY CROSS-LAYING A WARP OF SUBSTANTIALLY PARALLEL CONTINUOUS MONOFILAMENT STRANDS WITH A PARTIALLY FIBRILLATED OPNE NETWORK HAVING A PLURALITY OF INTERCONNECTED PARALLEL CONTINUOUS MONOFILAMENT STRANDS AT AN ANGLE OF 90* TO THE WRAP AND BONDING THE SAME.

Jill. 30, 1973 c, w, K|M 3,713b94-2 FROCESS FOR PREPARING NONWOVEN FABRICS Filed Duo. 16, 1969 4 Sneets-Sheet 1 CHARLES w. KIM 3 INVENTOR.

ATTORNEY Jill. 30, c, w K

PROCESS FOR PREPARING NONWOVEN FABRICS 4 Sheets-Sheet 3 Filed Dec. 16, 3.969

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CHARLES W. KIM INVENTOR,

BY Mm X ATTORNEY Jill. 30, 1973 c, w, M 3,713,942

PROCESS FOR PREPARING NONWOVEN FABRICS Filed D00. 16, 1969 4 Sneets-Sneet 5 CHARLES W. KIM INVENTOR.

ATTORNEY Jan. 30, 1973 c, w, K|M 3,713,942

PROCESS FOR PREPARING NONWOVEN FABRICS Filed Dec. 16, 1969 4 Sneets-Sneet 4 FIG. 8

CHARLES W. KIM INVENTOR.

BY AULQQQM XW- ATTORNEY 3,713,942 PROCESS FGR PREPARING NUNWUVEN lFABRlQS fiharles W. Kim, Wilmington, Del assignor to Hercules incorporated, Wilmington, Del. Continuation-impart of application Ser. No. $43,561, daily 22, 19%. This appiicaiinn Bee. in, 1%), Ser. No. 885,595

' lint. Cl. BfiZb 31/08 US. Cl. 156-252 2 @laims ABSTRACT UP THE DISCL JSURE Nonwoven fabrics are prepared by cross-laying a warp of substantially parallel continuous monofilarnent strands with a partially fibrillated open network having a plurality of interconnected parallel continuous monofilarnent strands at an angle of 90 to the warp and bonding the same.

This is a continuation-in-part of copending application Ser. No. 843,561, filed July 22, 1969.

This invention relates to a process for the preparation of nonwoven fabrics.

Nonwoven fabrics are textile fabrics which are neither Woven, spun, nor made by conventional wool felting processes. Rather, they consist of an aggregation of staple textile fibers interlocked to form a mat-like structure. Typical applications where these fabrics find utility include filter cloths, clothing insulation, carpet backing, gasket material, blankets, doilies, dish cloths, surgical dressings, pennants, inner-soles for shoes and many others.

Several processes are presently known for preparation of non-Woven fabrics. In one such process, the fibers are slurried in water or a similar inert liquid, the slurry is spread uniformly on a flat surface, the inert liquid is drained off and the web is dried under pressure to form a loosely associated web of randomly arranged fibers. In another process, dry fibers are laid on a solid flat surface, as a conveyor, by mechanical means such as, e.g., a carding machine. This dry process can be used to lay down the fibers in either a random or oriented arrangement. To impart strength and cohesion to the fiber mass, a bonding step is carried out by chemical or mechanical means. A thorough discussion of the preparation of nonwoven fabrics as presently practiced can be found in Nonwoven Fabrics by F. M. Buresh-Reinhold Publishing Co., New York, NY. 1962.

It is the object of this invention to provide a new and improved method of preparing nonwoven fabrics. The new and improved nonwoven fabric made is comprised of a plurality of substantially parallel, low denier, continuous monofilament strands of a synthetic thermoplastic polymer in the warp direction, having a plurality of substantially similar strands cross-laid on at least one surface thereof and making an angle between of 90 with said warp direction strands, said cross-laid strands being of the same or different thermoplastic composition and being bonded to said warp direction yarns at their cross over points therewith, said fabric having a weight between about 0.1 and ounces per square yard.

Preferably, the denier of the filaments will be between about 1.5 and and more preferably no higher than about 15. Higher denier filaments can be employed in the Patented Jan. 3Q, 3873 process, but fabrics resulting therefrom are less desirable as they will be too still for most applications where nonwoven fabrics are employed.

Nonwoven fabrics meeting the above description are unique in the art in that they are made up entirely of low denier, continuous monofilament yarns in both the warp and cross direction. This factor results in several property advantages over prior art nonwovens whether based on staple fibers, continuous multifilament yarns or spun yarns. For Example, these fabrics har e greater covering power per unit Weight than would a similar fabric prepared from a multifilament yarn, due to individual monofilaments being situated side by side rather than in bundles as would be the case with a continuous filament yarn or with synthetic staple fibers. For this reason, one can prepare a stronger product using this technique since each individual filament can be bonded at the crossover point rather than bonding just a relatively few filaments on the outside of a yarn bundle. Thus, there can. be a greater number of bonds per unit area as well as per unit weight than are normally possible With other nonwoven types. The strength of such fabrics is also improved by the presence in both the warp and filling directions of continuous filaments which are inherently stronger than spun yarns or staple fibers of the same denier. One further advantage of these fabrics accuring from the use of low denier monofilament strands is that a very pliable product can be formed-i.e., one having a high degree of drape.

The unique nonwoven fabrics made according to this invention can be prepared by a lamination process employing warp and cross-laying beams of substantially parallel continuous monofilarnent strands. In brief, this process comprises laying down a warp of substantially parallel, low denier continuous monofilament strands and cross-laying said warp at an angle between of with a plurality of similar substantially parallel continuous monofilament strands, and bonding said strands at their points of cross-over with one another. In a preferred embodiment of the process of the invention, the substantially parallel continuous monofilament strands are the product resulting from fibrillation of striated film.

The concept of fibrillating a striated film has recently been introduced into the art as a method of preparing low denier monofilaments. The striations in such a film provide precisely defined lines of weakness in a direction substantially parallel to the longitudinal axis of the film, i.e., parallel to the direction of orientation. When this film is subjected to mechanical working to cause splitting, such splitting is confined to the thin areas and the thick areas can be separated as continuous filaments. These films can be either oriented parallel to the striations or unoriented when they are subjected to fibrillation. Whether or not they are oriented is determined by the intended end use.

The mechanical working can be sufiicient to effect a complete fibrillation of the film. in such a case, the product is a plurality of individual, unconnected, parallel continuous monofilaments. If the mechanical working is discontinued prior to complete fibrillation, the product is a network of parallel continuous filaments interconnected by means of tiny side fibrils, the fibrils being the residue of the thin web section of the striated film. The resulting net-like structure is also useful in the process of this invention. This partially fibrillated film can be expanded up to about five times its initial width without breaking the interconnecting fibrils. Obviously, the extent to which it is expanded or opened out will effect the porosity of the nonwoven fabric prepared therewith.

In order to prepare a nonwoven fabric from one of these fibrillated products, two or more of the same are cross-overlayed and bonded. Nonwoven fabrics can be prepared in this manner having a variety of porosity levels, depending upon the degree to which the partially fibrillated films are expanded to open out their netlike structure or upon the number of layers which are laid up.

The invention can be described more clearly by reference to the attached drawing, in which:

FIG. 1 is a view of a section of a striated film with the size of the striations greatly exaggerated;

FIG. 2 is a schematic illustration of one method of fibrillating a striated film for use in the invention;

FIG. 3 is a perspective view of an expanded network structure produced by the partial fibrillation of a striated film;

FIG. 4 is a schematic illustration of one method of accomplishing the laminating process and subsequent bonding of the laminated structure;

FIG. 5 depicts a typical nonwoven fabric which can be prepared by the process of the invention showing one section somewhat magnified;

FIG. 6 is a schematic illustration of another process which can be employed;

FIG. 7 depicts an alternative method oflaying up the strands, and

FIG. 8 depicts another alternative method of laying up the strands.

The striated film which can be fibrillated for use in this invention is illustrated in FIG. 1. It comprises a thin strip of thermoplastic material 1 such as polypropylene, which is provided with a series of substantially uniformly spaced parallel ribs or striations 2 running longitudinally thereof and interconnected by webs 3 of reduced thickness. The film can be oriented uniaxially in the direction parallel to the striations. With uniaxial orientation, the tensile strength in the direction of the axis of orientation is greatly increased while the strength transversely is reduced so that the film can be readily split lengthwise. In comparison with the webs, the striations have a relatively high resistance to splitting, so that lengthwise splitting of the film is confined to the webs and the resulting filaments correspond generally to the striations.

In FIG. 2 there is illustrated, schematically, a method and apparatus for carrying out the fibrillation of the striated film for use in this invention. As illustrated in FIG. 2, the striated film 1 is advanced by draw rolls 4 from feed rolls 5, these two sets of rolls defining be tween them a fibrillation zone. The section of striated lm within this fibrillation zone is held under tension and angled over a triangle-shaped rotatable bar 6, having serrated edges 7, mounted in a suitable framework and driven by suitable drive means (not shown). As the bar is rotated in the direction of arrow A, the serrated edges are successively brought into engagement with the ribbon along lines transversely thereof with each successive line of engagement spaced upstream of the ribbon from the preceding line of engagement. After engagement, the serrated edge is advanced along the ribbon and then carried out of engagement with it. With the ribbon under tension, the teeth of the serrated edges bear upon and penetrate the ribbon, separating it into filaments which are thereupon taken up on a beam (not shown).

The degree of fibrillation effected on the film is regulated or controlled by the amount of contact between the serrated edges of the beater bar and the film. Thus, to effect partial fibrillation the apparatus is operated in such a way that the serrated edges of the bar are not in contact with the film continuously. This can be accomplished, e.g., by rotating the bar at a low rate as compared to the linear rate of advancement of the film. The

precise ratio of speeds is dependent upon the number of serrations per inch along the edge 7 relative to the spacing of the striations on the film and the number of such serrated edges on the bar. The degree of fibrillation can also be varied by varying the are through which the teeth travel while in contact with the film. To effect complete fibrillation, these factors are combined in such a way as to assure substantially continuous contact between the film and the beater bar, or contact between them at substantially every point along the surface of the film.

The product of partial fibrillation shown in FIG. 3, comprises backbone filaments S which correspond to the thick sections 2 of the striated film and interconnecting fibrils which correspond to the webs 3 adjacent to said thick sections, which webs have been split but not completely severed from their respective backbone filaments. These parallel backbone filamments are thus readily aligned in spaced apart relation, as they are shown in FIG. 3, by simply spreading the net-like structure.

In the method depicted in FIG. 4 for laying up layers of the fibrillated film, a plurality of substantially parallel monofilaments indicated generally at 10 are drawn from one or more supply beams 11 by means of pinch rolls 18 onto a stationary mandrel 13 to form a warp. The strands are aligned in a horizontal plane as they leave the beam, but are passed through an annular former 12 which conforms them to the shape of the mandrel 13 so that the complete surface of the mandrel is covered by the filaments as shown in the area designated by the letter M. As the filaments 1% are advanced parallel to the surface of the mandrel 13, a plurality of small denier monofilaments 14 is laid on them from one or more supply beams 15, supported on a rotatable carrying means 16 and adapted to orbit the mandrel 13 at a rate correlated with the rate of advancement of the warp monofilaments 10. By the combination of the rotating motion of the carrier and the forward motion of the warp filaments, the cross filaments can be laid on the warp filaments at an angle between about 2G and about 89. The now-laminar structure is drawn off the mandrel and compressed by pinch rolls 18 into a fiat structure 17 composed of a center layer comprising the parallel warp-type filaments and a surface layer of parallel continuous filaments disposed at an angle to the center layer.

The pinch rolls employed to advance the fabric structure from the mandrel and compress the same can be heated to a temperature sufficient to effect the necessary degree of bonding at filament crossover points if bonding can be effected without the addition of an extraneous adhesive material. This can be the case, e.g., where the fabric comprises a mixture of thermoplastic materials, such as a. mixture of polypropylene and a propyleneethylene copolymer which softens at a lower temperature.

In a case where an extraneous adhesive is to be employed, it can conveniently be added following flattening of the structure by means of, e.g., spray nozzles 19, followed by drying and baking in an oven 20. Upon leaving the oven, the completed fabric 21 is collected into a mill roll 22 at a take-up station 23.

A section of the completed fabric is shown in FIG. 5. The warp yarns 25 are shown substantially parallel to one another along the longitudinal axis of the fabric with cross-direction filaments 26 substantially parallel to one another but disposed at an angle, 6, to the warp filaments. The dotted lines represent the extremities of the cross-laying beams on the opposite surface of the fabric.

Useful nonwovens can be prepared according to this embodiment of the invention with the cross-laid filaments disposed at an angle between about 20 and 89 to the warp filaments. Preferably the angle should be at least 45. As the angle gets smaller, the fabric gets weaker, since the reinforcement afforded by the crossing filaments becomes less. The angle between the filaments in the warp and cross directions using this embodiment is determined by the ratio of the speed at which the warp filaments are advanced to that at which the cross-direction filaments are wrapped around them.

With reference to FIG. 5, the dimension R is the pattern repeat distance, i.e., the linear distance of the warp which will be cross-laid by a single cross-laying beam in 6 hesive solution, emulsion or dispersion is applied thereto. They are then drawn over forming mandrel 13 and overlaid with cross-direction strands in the manner described above. The mandrel is heated to cure the adhesive and bonding of the layers is effected while the strucmalring one complete orbit around the forming mandrel, ture is in tubular form in contact with the mandrel. When which is expressed by: this embodiment is employed, the former and the forming mandrel should be treated as with an inert, non-ad- R= fi g x herent coating, to prevent the adhesive from adhering Spee 0 cross amen S the filaments thereto. Upon leaving the mandrel, the tu- Thus, using basic trigonometric relationships, it can be bular structure can be slit along one or both edges by seen that: means of a slitting knife 31 installed immediately ahead of pinch rolls 18. This form of the structure can then be cot 0= warlp .g opened out to form a fabric comprising parallel longipee 0 crossat aments W tudmal filaments overlald with continuous cross-direcf tron filaments on only one of its surfaces. ThlS fabric, of

F thi l ti hi 0, th ngl b t th warp course, will have only half the thickness and half the and cross filaments, can readily be determined for any Strength of that P p according to t Will combination of speeds and fabric widths, likewise be more flexible and more drapeable.

By reference to FIG, 5, it will also be seen that, in In the embodiment Of the invention depicted in FIG. 7, order to cross-lay the fabric completely, so that succesthe ts are drawn Off supply beam 33 by a set of sive wraps of cross-laying filaments are contiguous to pinch rolls 34 to form a warp between a pair of continuone another, the required number of cross-laying beams ous endless wire belts or cables 35 and 35. The crossis a function of the pattern repeat distance (R) and the filaments are pp from beams 36 adapted rotate width (W of the cross-laying beam and can be expressed around the W rp and the bolts 35 and 35 Where they are b h ti held to prevgnt their puckeulijg the wlarp. The structure t us prepare 1s compresse y pinc rolls 34 to retain number of CrOSSJaymg beams it and the cross-filaments are slit to remove them from speed of Warp filam n the belts, allowing the belts to continue their revolution, speed of cross-laid filaments while the fabric is advanced away from them. The fabric width of cross-laying beam (W,,) can be bonded by the pinch rolls, if desired, or the fab- In the following table are listed examples of combinations 5:2 3: firs 5321: 36mg w a iia ahii hr sss h laiggh g of the above variables determined as set forth above for using this embodiment is determined as explained here several operating runs for preparing fabrics according to inabove. this invention, assuming a constant fabric width of 4 feet. 35

Width of Speed of Pattern cross- Number of Speed of crossrepeat laying cross-layer warp, layer, distance, package, packages f.p.m r.p.m. it. ft. required 0 s 1 s 1 8 8 s 1 1 1 8250 10 5 1 5 5750 50 25 2 1 2 7550 50 50 1 1 1 8250 50 100 is 1 y, 8630 50 5 10 1 10 3830 7 50 7/50 7/50 1 89 25 50 y pg 1 8630 As indicated above, the fabrics can be bonded by heat The cross-filaments can also be laid down at an angle alone which can be applied by means of the pinch rolls 50 of 90 to the warp filaments. For example, in the em- 18, or they can be bonded by means of an adhesive. The bodirnent pictured in FIG. 8, a warp beam 40 is fed from adhesive can be an emulsion, dispersion, or solution of a a warp supply roll 41 by pinch rolls 42 onto a moving heat activated material which will adhere to the polymer. continuous belt 43 to calendar rolls 44. The advancement This adhesive is activated by heat applied in the drying of the warp is periodically interrupted an a cross-filament oven. Alternatively, small particles or fibers of a thermosupply beam 45, actuated by reciprocating apparatus, not plastic resin can be employed as the adhesive. These are shown, is rolled across the warp at a 90 angle thereto dusted onto the fabric, then melted in the oven and they and lays the cross filaments thereon, whereupon the severthen fuse to bond the fabric upon cooling. ing means 46, e.g., a hot wire, is actuated to sever the Bonding can also be effected by the ultrasonic technique laid-out cross-filaments from their supply beam. The sup- In this method, the unbonded structure is contacted With ply beam is then returned to its original position and the an ultrasonic horn which causes melting at only the point warp beam, now carrying laid-over cross-filaments, reof contact of the horn. Such contact at points were sumes its advance and the cycle is repeated. The nonfilaments cross causes fusion of the filaments at that woven structure is then subjected to heat to effect bondpoint. Other bonding techniques are known to the art and ing as, e.g., by means of calendar rolls 44 or by other any technique suitable according to prior art practice bonding means as discussed previously and is advanced is useful with the materials of this invention. to a rewind station, not shown. Inasmuch as the appara- Chemical bonding, however, is prefered, i.e., Where an tus for carrying out the above process is not a part of adhesive material in solution or suspension is applied to the invention, and is within the skill of the mechanical the structure and cured by heating. The adhesive to be design art, further description of the reciprocating means used can be selected from a wide variety of commercially for the cross-filament beam, the severing means, and the available materials, depending upon the identity of the synchronization means for these members is not shown thermoplastic polymer being employed in the fabric. here.

In the apparatus for carrying out the invention depicted As has been indicated previously, a striated film can be in FIG. 6, the small denier monofilaments 10 are drawn completely fibrillated to the point where each filament is from supply beams 11, over a coating roll 30 where an adan entity totally unconnected to any neighboring filament,

or it can be only partially fibrillated to form an expandable network structure as depicted in FIG. 3. Either the partially or completely fibrillated product can be ernployed as the low denier monofilament strands employed in this invention. They can be handled in the same manner and they perform in the same manner except that the incompletely fibrillated product results in a slightly stiffer fabric than that prepared from completely fibrillated, completely separate filaments.

Although the invention is described in terms of preparing the novel fabrics from filaments resulting from fibrillation of striated films, it should be clear that this is not a limitation on the same. Individual, small denier monofilament strands from any source can be employed so long as they can be collected on a beam and drawn off in substantially parallel fashion onto the forming mandrel. The emphasis on fibrillated striated films is intended as a recognition that the fibrillation technique represents the most practical method yet devised for preparing the required starting material.

Nonwoven fabrics according to the invention can be prepared from filaments of any of the conventional thermoplastic fiber-forming polymers. Exemplary of such materials are polypropylene, nylon, polyesters such as poly- (ethylene terephthalate) and acrylics such as polyacrylonitrile and the like. Moreover, blends of these various polymeric filaments can also be employed when specific combinations of properties are desired. It is also feasible to employ bi-component filaments having components of differing properties as, e.g., differential shrinkage to increase the bulk of the product or different melting points to facilitate bonding. The composite or bi-component technique also can be advantageous in imparting latent crimp to the fibers. When such fibers are heated and their bulk increases, they exhibit substantially higher covering power. It is also possible, if desired, to employ foamed filaments.

Nonwoven fabrics prepared by the process of this invention can be employed in any of the applications where nonwovens are conventionally employed. One such application is in the preparation of reinforced paper where a web of pulp is laid on either side of the nonwoven fabric and calendered to the proper thickness. Such reinforced paper is attractive in, e.g., preparation of certain types of disposable garments, in that it has excellent drape properties due to the long, fine denier filaments in the reinforcing fabric. Other applications for the nonwovens prepared by the process of the invention include bagging, filter fabrics, and carpet backing.

The specific mechanical embodiments of the invention disclosed herein relating to the fibrillation of the striated film and to the overlaying of the lamina are intended as illustrations only. The invention is not limited to these methods.

What I claim and desire to protect by Letters Patent is:

1. A method of preparing a nonwoven fabric which comprises:

providing a partially fibrillated open network having a plurality of spaced apart substantially parallel continuous monofilament strands, adjacent ones of which are interconnected by a plurality of fibrils, said fibrils having a cross-sectional dimension substantially smaller than the cross-sectional dimension of said monofilament strands;

advancing a warp of substantially parallel, continuous monofilament strands from a first source of supply; intermittently interrupting the advancement of said warp strands;

advancing said open network from a second source of supply and laying said network on said warp at a angle to said warp;

severing the network from its source of supply to form a two-layer structure over the width of said warp, said fibrils serving to maintain the Strands of said network in substantially parallel relationship to each other and in 90 relationship to the warp strands; and

applying heat and pressure to the advancing two-layer structure to bond the warp strands and the network at their crossover points.

2. A method of preparing a nonwoven fabric which comprises:

providing a first and a second partially fibrillated open network, each having a plurality of spaced apart substantially parallel continuous monofilament strands, adjacent ones of which are interconnected by a plurality of fibrils, said fibrils having a cross-sectional dimension substantially smaller than the crosssectional dimension of said monofilament strands;

advancing said first open network in a warp direction from a first source of supply;

intermittently interrupting the advancement of said first network;

advancing said second open network from a second source of supply and laying said second network on said first network at a 90 angle to said first network;

severing the second network from its source of supply to form a two-layer structure over the width of said first network, said fibrils of said second network serving to maintain the monofilament strands of said second network in substantially parallel relationship to each other and in 90 relationship to the monofilament strands of said first network; and

applying heat and pressure to the advancing two-layer structure to bond the monofilament strands of said first and second networks at their crossover points.

References Cited UNITED STATES PATENTS 3,314,841 4/1967 Romanin 156253 3,515,621 6/1970 Watson 156181 X 1,949,159 2/1934 Glidden et al 156-252 X 3,132,986 5/1964 Goldman 156-169 X 2,332,848 10/1943 Grabec 156252 X 3,386,876 6/1968 Wyckoff 156-252 X 2,895,535 7/1959 Ono 156181 X 3,273,771 9/1966 Beaumont 57155 UX 3,250,655 5/1966 Adler 156181 3,345,230 10/1967 McClean 156-18l 3,405,027 10/1968 Wyckotf 156252 X 3,444,025 5/1969 Hillas 156178 X 3,445,319 5/1969 Dawbarn 156-177 X FOREIGN PATENTS 13,430 6/1908 Great Britain 156-180 982,420 1/1951 France 156-169 587,968 5 1947 Great Britain 156-252 337,362 5/1921 Germany 156-259 CARL D. QUARFORTH, Primary Examiner R. GAITHER, Assistant Examiner US. Cl. X.R. 

